Electronically scanned arrays (ESAs) may be set up with phase shifters servicing elements and subarrays steered by adjustable time delay. Subarray combinations may be in either an analog or digital sense. Digital combination allows limited scan, multiple full aperture beams. Beams may be steered electronically through corresponding settings in both the phase shifters and adjustable time delay elements.
An exemplary array may be arranged horizontally and be horizontally subdivided into a number of horizontally adjacent subarrays. The array elements may be arranged in horizontal rows and vertical columns. All of the subarrays typically extended the full vertical height of the array. Horizontally contiguous subarrays do not share elements with adjacent, contiguous subarrays. Horizontally overlapping subarrays may share elements with adjacent, overlapping subarrays.
For example, in the case of uniformly-sized subarrays with 50% horizontal overlap, an array which is horizontally adjacent to two other arrays will share the left half of its elements with the horizontally adjacent array on its left and the right half of its elements with the horizontally adjacent subarray on its right. In the area of overlap, the arrays overlap throughout the full height of the array. Overlapped subarrays may decrease the width of respective subarray beam patterns and may provide some degree of grating lobe suppression.
Shared-element, overlapping, full-height subarrays may be more costly to manufacture and introduce an added level of complication to achieve desired calibration of the array, in comparison with non-overlapping full-height subarrays. A complex, calibration correction term associated with a single array element location may be applied to multiple signal paths if the element is shared between two subarrays. For 50% overlap, for example, two signal paths may be required. Elemental phase shifters may perform electronic beam steering in the vertical orientation along with associated array calibration for signals in one of two subarrays by which the column of elements is shared. For the other subarray, a manifold phase shifter may apply an additional calibration setting for the signal path to the other subarray.
The additional manifold phase shifters required for more optimal calibration may increase costs and add complexity to the array architecture. Subarrays with a higher percentage of overlap result in a greater number of parallel signal paths with a corresponding requirement for additional phase shifters to achieve desired levels of calibration. As a result, array architecture may be more complex because a manifold phase shifter may be required to account for differences in signal path for shared-element signal paths in adjacent sub-arrays. The use of such overlapped subarrays may therefore result in increased complexity where optimal calibration is desired.
It may also be desirable to form an elevation difference beam. In the case of a full-height array, creating an elevation difference beam may add further architectural complexity.